1. Field of the Invention
The invention is concerned with the fabrication of integrated circuits.
2. Description of the Prior Art
Integrated circuit technology is largely dependent on methods for depositing metallic films on substrates and for patterning such films. Substrates typically consist of electrically insulating materials such as alumina or glass. Film deposition and film patterning are typically carried out as separate, consecutive steps and may be applied repeatedly to deposit layer upon layer of different metallic films in the manufacture of an integrated circuit device.
Films may be deposited, for example, by vacuum deposition and the pattern may be made by selective exposure of the deposited film to a chemical etchant which is typically accomplished by applying a mask to the film prior to its exposure to the etchant.
A difficulty which arises primarily with the etching of noble metals lies in the tendency of etchants such as aqua regia to locally detach the mask from the film which, in turn, leads to poor pattern delineation.
One method designed to overcome this difficulty is disclosed in U.S. Pat. No. 3,451,813, issued to L. C. Kinney et al. on June 24, 1969. Using a binder, Kinney coats the substrate with a photoflash sensitive metal compound such as silver oxide, copper oxide, or nickel formate, places a transparency mask on the coated substrate and exposes the resulting assembly to a flash of light to reduce the exposed portions of the coating to elemental metal. Alternatively, a metallic powder such as copper powder or platinum powder may be deposited on the substrate followed by fusing the metallic particles into a coherent layer by photoflash.